Subsea hydraulic couplings are old in the art. The couplings generally consist of a male and female member with seals positioned within the female member to seal the junction between the male and female members.
The female member is generally a cylindrical body with a relatively large diameter longitudinal bore at one end and a relatively small diameter longitudinal bore at the other. The small bore facilitates connections to hydraulic lines, while the large bore contains the seals and receives the male portion of the coupling. The male member includes a cylindrical portion at one end having a diameter approximately equal to the diameter of the large bore in the female portion of the coupling. The male member also includes a connection at its other end to facilitate connection to hydraulic lines. When the cylindrical portion of the male member is inserted into the large bore of the female member, according to the various embodiments of the device, the seals, generally resembling O-rings, either abut the end, or face, of the male member or engage the male member about its circumference. The hydraulic fluid is then free to flow through the female and male portions of the coupling, and the seals prevent that flow from escaping about the joints in the coupling.
In some instances a check-valve may be installed in the female member and also in the male member. Each check-valve is opened when the coupling is made up, and each check valve closes when the coupling is broken so as to prevent fluid from leaking out of the system.
The seals most commonly used in the past have been an elastomeric material and such seals have numerous disadvantages. The principal disadvantages are: (1) the inability of the seal to withstand the deteriorating effects of a subsea environment for extended periods of time, and (2) the inability of the soft seal to contain the higher pressures being imposed on the hydraulic systems.
Metal seals have been developed to better withstand both the deteriorating effects of the environment and higher pressures. One such seal is a crush type which is positioned between the end of the male portion of the coupling and the internal end of the large bore in the female portion. When the male portion is inserted into the female, the metal seal is crushed between the two portions and a seal is effectuated between the two. In view of the crushing action, the seal can be used only once. If the coupling is separated for any reason, the once used crushed seal must be replaced with a new seal. Also, the male and female members must remain fully engaged to prevent leakage around the seal.
Another type of metal seal has been employed for sealing between the end face of the male member and a shoulder in the bore of the female member. The seal has a cavity which is exposed to pressure in the coupling and, in response to that pressure, the seal tends to expand longitudinally to effectuate the seal between the end face of the male member and the shoulder in the female. This longitudinal expansion of the seal tends to force the male member out of the bore of the female member. To overcome the tendency for the male and female members to part, and to ensure a sealing relationship of the seal with the male and female members prior to pressurization of the coupling, an external preload mechanism is used which holds the male and female members together. The drawback to this apparatus is that if the internal pressure exceeds the holding capacity of the external preload mechanism, the male and female members will part sufficiently to break the sealing relationship with the metal seal. Also, external preload mechanisms are expensive and require considerable space for mounting in a subsea environment. The complex mechanism affords greater possibility of the problems and malfunctions.
U.S. Pat. No. 4,637,470 to Weathers et al. shows a subsea hydraulic coupling having a metal seal ring between the end face of the male member and a shoulder in the bore of the female member. The seal is V-shaped in cross-section, the lips of the V being exposed to pressure in the coupling and tending to expand longitudinally to enhance the seal between the male member and female member shoulder. The Weathers coupling includes Belleville washers which are used to preload the seal upon connection of the members, before pressurization. The preloading helps prevent leakage at low pressure. The Belleville washers exert a longitudinal force against the opposing member, in order to maintain the metal seal ring in tight contact between the members. As discussed above, the preload mechanism is expensive and complex.
The male and female portions of the above face-type couplings are each one piece devices, and the seal rests at or near the end face of the male portion. Particularly in the case of the face-type seals, there is a danger that the seal will blow out of the female section and be lost if the coupling is parted under pressure. The Weathers coupling described above discloses a retainer for holding the seal in place. The retainer is an elastomeric ring member secured within a groove formed in the bore of the female member. Even with the elastomeric ring, there is a risk that the metal seal will blow out due to pressure when disconnecting the coupling.
Another type of annular metal seal is a pressure energized annular seal which seals between the outer longitudinal surface of the male member and the bore wall of the female member. Such a seal is shown in U.S. Pat. No. 4,694,859 to Robert E. Smith III. The annular metal seal is trapped within the female body by means of an internal retainer which holds the seal against a shoulder in the female member bore. When the retainer is inserted and held in place by a clip, it preloads the metal seal by slightly compressing the seal to force it to expand radially against the male member surface. The male member is designed to be inserted through the retainer and through the metal seal so that the seal engages the circumferential surface of the male member in a sealing relationship. A cavity in the seal is exposed to internal coupling pressure to enhance the effectiveness of the seal.
Still another coupling and metal seal is shown in Applicant's pending application Ser. No. 085,982, filed Aug. 14, 1987. This coupling shows an internally preloaded metal-to-metal seal hydraulic connector, in which the sealing surface is preloaded from within the coupling itself. The seal is a metal-to-metal seal between the ground surface of the male member leading face and a mating seal seat in a sleeve member. The sleeve member is allowed to slide longitudinally in the female member bore. As the male member end face is pressed against the sleeve member, the sleeve member pushes against the bias of an internal preloading device shown as a spring washer. Before pressurization, the preloading device helps obtain a metal-to-metal seal between the leading face of the male member and the seal seat on the internal bore of the sleeve member. Upon pressurization of the coupling, the sleeve member is pressure energized to slide longitudinally against the leading face of the male member. This longitudinal movement enhances the seal. The metal-to-metal seal between the end face of the male member and the seal seat in the sleeve member is not replaceable, but requires re-machining of the mating surfaces should those surfaces become damaged.